Many receivers, including OFDM receivers, utilize ML demapping to extract the transmitted symbols from received signals by performing a search process. In MIMO systems in which two or more data streams are concurrently transmitted by two or more transmit antennas, ML demapping becomes very processing intensive, conventionally requiring a very large number of multiplications. In the case of 64-QAM (quadrature amplitude modulation), the ML demapping operations conventionally require 64T-point searches for each OFDM tone, wherein T is the number of transmitted information streams. In the case of two streams, a 4096 point search would be required. This very large number of multiplication operations increases the complexity, cost, and power consumption of OFDM receivers.
Thus, there are general needs for methods and OFDM receivers that can extract the transmitted symbols from two or more transmitted streams with reduced complexity, cost and/or power consumption. There are also general needs for methods and OFDM receivers that can extract the transmitted symbols from two or more transmitted streams with a reduced number of multiplication operations.